Expressions like 'Eagle-eyed' and 'Eyes like a hawk' have been in the English language for aeons. This is not without cause. It is arguable that birds of prey have the keenest vision of any living creature.
With up to a million cones per square millimetre of fovea (an area of the retina with the greatest concentration of receptors), bird of prey, without having magnified vision, enjoy visual acuity around eight times that of humans. So large are the eyes that no raptor is able to move the eye within its socket. It has to rely on head movement to build up a three dimensional picture of its world.
Raptors have up to 50% binocular vision which gives good judgement of depth and distance. Coupled with the ability to process overlapping images in the brain this affords the high level of accuracy needed to catch fast-moving or well-concealed prey.
Many raptors have a bony ridge above the eye. Rather than being there to make them look even more fierce, its purpose is to protect the eye when the bird is working to subdue its prey, and to give the eyes some protection from the sun. At these, and other times, the 'third eyelid' or nictitating membrane is also deployed to protect the eyes. This tough, opaque membrane is used as a protection device, and also serves to keep the eyes clean and clear.

The ears

Diurnal raptors have a level of sensitivity to sound and can accurately detect direction. Owls are equipped with ears of different sizes, placed at different heights on either side of the face, to which sound is funneled via the facial disks. It is also possible that the range of audible sounds varies between the ears. This arrangement allows them to pinpoint with a very high level of accuracy the exact source of a sound. In some cases the bird can attack successfully, a small creature like a mouse under 12' of snow!

The beak

Most, if not all birds of prey use the beak for tearing their food apart. The beak is not designed for killing. The only possible exception to this is in the case of falcons. Falcons have a protrusion on the upper mandible, just behind the curve of the beak, and a matching depression in the lower mandible. These are applied at the base of the skull of their prey, and are used to sever the spinal cord after the prey has been caught. Some holdingpattern of kite, that specialise in lizards, have a similar arrangement. Other species, such as the snail kites, have evolved a greatly extended point to the upper mandible, to enable them to sever the shell closing muscles of molluscs and extract them from their shells.
The relative size and shape of the beak on a raptor can be an indication of its major food source, and its method of hunting. Large vultures and condors are equipped with a very powerful beak to tear into the thick skin of large carrion.
Many owls appear to have quite short beaks, but in fact all owls are mostly feather, and there is a good deal of beak concealed behind the facial feather covering. The short, bristly feathers around the mouths of owls are incredibly sensitive, and are used by the owl to 'feel' for its food, as its eyes will almost invariably be closed when eating, as a method of protection.

The feet and talons

These vary enormously between species.In all cases they are, in relation to the size of the bird, very powerful. The lower leg or tarsus usually acts as a channel for tendons from the upper leg muscles to the toes and claws. The tarsus is typically short and robust where the prey is substantial and long and thin to give longer reach for those birds capturing aerial prey. The Secretary Bird has extremely long legs and stubby toes that enable it to disable its prey with a powerful, well aimed kick.
The structure of the foot also varies enormously. Scavengers, such as vultures, have long slender toes that are clearly designed only for walking. Predators of robust prey like mammals have thick toes and well curved talons, giving a very strong, well-anchored grip. Sparrow hawks and falcons have long, slender toes, needle-sharp and well-curved talons and toe pads with protrusions that match the tips of the talons, giving maximum reach and grip. Fish-catching species have the longest and most curved talons. Coupled with spiny scales on the toe pads, these give maximum grip on wet, slippery prey.

The wings

Most raptors require good powers of flight to cover their large home ranges and, in many cases, to allow them to pursue their prey. Wing shapes fall into three groups, broad, short and long.
Broadwings include Vultures, most Eagles and Buzzards. The wings are long and broad and are designed to allow the bird to soar effortlessly for long periods, using rising air currents.
Shortwings include hawk-eagles and most hawks. Many owls, particularly boreal owls, also fall into this category These birds need to be fast and very manoeuvrable. For this they have good lift characteristics combined with dexterity and a long tail that permits tight, fast turns through the trees.
Longwings are the falcons. Their wings are designed for speed, and the large pectoral muscles drive them over large distances at an impressive rate. The tail length is variable but never short, tending to be longer in the kestrels, where it also acts as an aid to hovering, and in certain species of falcon whose lifestyle dictates tight turns.